The first ? I have is what make, model and year auto is going into. Next is why not check JC Whitney for the wire harness module.

If you know what the car voltage is you must have a volt meter? Check the voltage across the amp the salesman paralleled to with your cd player attached. Check the voltage across the connections to your cd player when attached to your car power. If there is a difference and it still is not working buy a cheap zener diode at your local electronics store that is rated for the difference in voltages and insert in the line, observing polarity to reduce the voltage accordingly. Probably not a voltage problem though. More likely a faulty ground in your car.

If the player was designed for in car usage at a nominal 12 volts, then car system voltages upto at least 15 volts should not harm it in the slightest, maybe even higher will be OK!!!

A car has rarely exactly 12 volts and almost never with a running engine and the battery and charging system in good working order.

Depending upon the make of car, the battery is generally charged at an end voltage of around 14.2 to 14.4 volts. a tick higher or lower could also be possible......its not really an exact science!!! No0r does it really need to be.....

It wont be anything to do with the different voltage. All batteries vary up to 14.5 V when fully charged and this would make no difference to the player. You need to look elsewhere for the problem. Get a volt / ohm meter and check through the system and you will probably find the fault is something as simple as a loose connection or blown fuse.

I have 15 years past exp. as a car stereo installer .

First , are you sure you are using the proper power wires to hook to acc. and bat.

Pioneer units are very sophisticated in there wiring needs and a proper manual is needed to hook it up correctly .

Maby a dumb question , but did you turn on the ignition key when you first tested it ?

If it worked for the salesman it should have worked for you if you wired it correctly.

Small voltage differences are not a problem , be sure you have a good ground .

Put inline fuses on the power wires if they are missing . Other wires to deal with ( besides the speaker wires ) are the illumination " usually yellow " and the amp trigger " usually pink ".

For a quick test simply connect acc.wire , bat. wire and illumination wire to pos. of any 12V battery and black ground wire to neg. of battery , turn on unit and should work . Dont leave unit on to long ( 1 min.) with unconnected speaker wires as the internal amps. will overheat .

Hope this helps .